os_support: Don't try to return the service name as a string in getnameinfo

Some systems may be lacking getservbyport; the previous ifdef wasn't
quite enough since it still assumed that struct servent was defined,
as pointed out by Clément Gregoire.

Simply remove the possibility to return non-numeric services in
getnameinfo; no caller of getnameinfo within libavformat
currently try to use getnameinfo for retrieving the port number without
NI_NUMERICSERV, and falling back on getservbyport may be non-threadsafe.
Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -1513,7 +1513,6 @@ SYSTEM_FUNCS="
     GetProcessMemoryInfo
     GetProcessTimes
     getrusage
-    getservbyport
     GetSystemTimeAsFileTime
     gettimeofday
     gmtime_r
@@ -4240,7 +4239,6 @@ fi
 
 if ! disabled network; then
     check_func getaddrinfo $network_extralibs
-    check_func getservbyport $network_extralibs
     check_func inet_aton $network_extralibs
 
     check_type netdb.h "struct addrinfo"

libavformat/os_support.c

@@ -204,16 +204,9 @@ int ff_getnameinfo(const struct sockaddr *sa, int salen,
     }
 
     if (serv && servlen > 0) {
-        struct servent *ent = NULL;
-#if HAVE_GETSERVBYPORT
         if (!(flags & NI_NUMERICSERV))
-            ent = getservbyport(sin->sin_port, flags & NI_DGRAM ? "udp" : "tcp");
-#endif /* HAVE_GETSERVBYPORT */
-
-        if (ent)
-            snprintf(serv, servlen, "%s", ent->s_name);
-        else
-            snprintf(serv, servlen, "%d", ntohs(sin->sin_port));
+            return EAI_FAIL;
+        snprintf(serv, servlen, "%d", ntohs(sin->sin_port));
     }
 
     return 0;